Jackson, Seminars in Perinatology 15:49 (1991), describes various procedures for prenatal diagnosis, including procedures to diagnose diseases. These procedures involve analysis of the DNA present in early embryonic stages. Specifically, Jackson mentions the use of a polymerase chain reaction to amplify genes, and the possibility of testing oocytes by polar body assay. According to Jackson:                “There are other conceivable embryo biopsy approaches for prenatal diagnosis. The trophectoderm may be obtained at later, multicellular embryonic stages when more cells might be obtained and induced to replicate in tissue culture . . . Another approach to early prenatal diagnosis is the recovery of fetal cells in the maternal circulation. This tantalizing possibility for a non-invasive method has been pursued for several years by groups in both the United States and the United Kingdom. Both groups originally sought placental immunologic markers for identification and recovery of these cells. Several trophoblast antibodies were developed, some of which appeared to have relative specificity for the fetal cell. After sporadic reports of success, recent articles appear to indicate that these markers are insufficiently specific and actually are attached to maternal cells frequently enough to make this approach unworkable to date.”        
Bianchi et al., Proc. Natl. Acad. Sci. USA 87: 3279 (1990), describe isolating fetal nucleated erythrocytes in maternal blood using a monoclonal antibody against the transferrin receptor. They state that they “were successful in detecting the Y chromosomal sequence in 75% of male-bearing pregnancies, demonstrating that it is possible to isolate fetal gene sequences from cells in maternal blood.”
According to Roberts, Science 18:378 (1991), two procedures available for prenatal screening are chorionic villus sampling (CVS) and amniocentesis. Both these procedures have problems involving waiting time and risk of miscarriage, “estimated at 1% to 2% for CVS and 0.5% for amniocentesis.” Supra. Roberts also points out a procedure for analyzing nuclear DNA directly when cells are in interphase.
Lohka and Masui, Science 220:719 (1983), describe inducing the formation of a nuclear envelope in demembraned sperm of Xenopus laevis using a cell-free preparation from the cytoplasm of activated eggs of Rana pipiens. 
Leno and Laskey, J. Cell Biology 112:557, (1991), performed experiments using erythrocytes from adult chickens. According to Leno:                “Coppock et al. (1989) [Supra] have reported that a pretreatment with trypsin was required for nuclear decondensation and DNA replication of Xenopus erythrocyte nuclei in egg extract. Trypsin pretreatment was not required for nuclear decondensation and DNA replication in our extracts.”        
Gordon et al., Experimental Cell Research 157:409 (1985), describe “a system for the activation of human sperm using cell-free extracts from Xenopus laevis eggs.” Similarly, an abstract, by Brown et al., J. Cell Biology 99:396a (1984), indicate that nuclear changes which occur during the early phases of fertilization can be stimulated by injecting isolated sperm nuclei into heterologous recipient eggs, or by incubating frog sperm nuclei in the presence of cell-free extracts from frog eggs. They state that they found human sperm can be activated in vitro using Xenopus laevis frog egg extract to stimulate the early events of nuclear activation, including chromatin decondensation, nuclear enlargement and DNA synthesis.